Telephone system.



PATENTED SEPT. 15,1903. Y

No. '138.78m`

s4. A. DUALL.. `TELEPHONE SYSTEM. `.APPLIGATION I'LD UGL, BL. 1902.

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UNITED 1 STATE-s Patented september 15, 1903; 5

STANLEY 'A. DUvALL, or CHICAGO, ILLINOIS.

TELEPHONE SYSTEM.

SPEGIFIGATION forming part of Letters Patent No. 738,780, dated September 15, 1903.

l Application led August 18, 1902. Serial No. 120,066. (No model.)

."To all whom t may concern:

Be it known that I, STANLEY A. DUvALL, a citizen of the United States, residing in the city of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Telephone Sysf` tems, of which the following is a specification. My, invention relates to telephone systems wherein the lines of subscribers are brought to a central point or points for interconnec-` tion, commonly known as exchange systems, and particularly to such systems as em-` ploy a common source of current-supply at each-such central point or station for signaling or talking, or both. ,p

My invention has for-its object-the simpli-V fication of the apparatus at the central office or exchange, the removaliof all coils from the talkingcircuit, and in general the improve` ment of the supply and control of the current employed for signaling and for talking. Heretofore in many of the bestsysterns of which I have knowledge it hasbeen common practice to use what are known as cut-off i relays, interposed usually in the connections from jacks to main battery and controlling the continuity of the line-circuits from the jacks `to the line-relays and to the main battery. Whenever aplugbyits insertion in any jack of a line closes the circuit of one of these cut-o'relays, the line-circuit is at once and automatically broken or cut off. I prefer,

. since contacts in the jacks are a necessity, to utilize them in controlling the line-relays di` "ssi rectly without the interposition of any other relays. This is the iirst improvement. I cause a short circuit around each line-relay t coil to be closed whenever a plug is inserted in any jack pertaining to that line. i In order to balance the lines, which is der sirable for many reasons, it has been customary to employ separate balancing resistances lin one side and the line-relay windings or ally'` been employed-that is, at any given timefor both signaling and talking. In

2 case of accident to this battery it would be ...quite possible to have an appreciable interruption of the exchange business before it could be iixed. Then, again, itis often desirable to have different voltages for talking and 'discharged cells will be boiled while the completely-discharged ones are receiving the necessary charge, Working a great injury to the cells. I prefer to connect two batteries in parallel when talking, one being at all times available for signaling and the other for talking. They may be of the same voltage; but inevery case if the signaling-battery is more nearly discharged than the other it will receive a charge during connection, and vice versa. The two batteries will reinforce each other in carrying their respective loads.

In common battery systems supervisory signals are employed associated with the plug cord-circuits, and the relays controlling these signals are usually placed in the cord conductors, being thus included in the talking-circuits. I prefer to make a bridged connection of my batteries to the cords, with the supervisory relays in the arms of the bridge, so that their impedance is useful to prevent the voice-currents from being repeated into other circuits through the battery connection and is removed' from the through talking-circuit with which they are associated.

Many other points will appear to those skilled in the art from a perusal of the'fola lowing specification, wherein the saine reference characters point out the sameparts throughout. l

Referring to the drawing accompanying this specification and forming apart hereof, the figure is a diagram "showing two subscribers lines connected to their terminal apparatus at a central office, With the connecting-circuits thereat, certain well-known elements, such as the listening and ringing keys, being omitted for the sake of simplicity.

In the ligure each line is shown with but a single jack; but it will be understood that this system is particularly applicable to multiple-board work and, in fact, is best adapted IOO - throughout with a prime-point.

thereto; but as the additional jacks would be the merest duplicates of those shown and simplicity in the diagram is essential they are omitted.

A and B are two subscribers stations connected to the central oliice by the metallic circuits 1 2 and 3 4, respectively. The apparatus at each subscribers station is the usual outfit, consisting of a -bell or ringer Q, normally connected-across in series with a condenser q in such manner that ringing-currents from central-will -nd a path, but continuous current from the battery will be exeluded. In a normally open bridge are included the telephone-receiver R and the transmitter T, this bridge being closed when the set is in use by means of the switch S, controlled by the receiver in the well-known way. The apparatus at station A being lettered as above, that at station B has the same letters At the central station the line conductors 1 and 2 are connected, respectively, to the springs j and j of the spring-jack J through the two windings of the line-relay Z. Between the relayf windings and the jack-springs the portions 8 and 9 of the line are connected by conducf tors 7 to the terminals of the signaling-bat-y tery B. Although for convenience of illustration this battery is shown in duplicate, it

will be understood that but one such battery is usually employed. The relay when energized pulls up its armature ZH to-close a local circuit extending from the 'armature and itsv contact-point Zlathrough lamp L and to batf tery B by wires 30.

At each side of the jack J a Contact is provided, the one, j4, being connected by conductor 5 to line-wire 2 outside the line-relay Z and the other, j5, being similarly connected by conductor 6 to line-wire 1. When a plug is inserted in the jack J, the springsj andy"` are spread apart to make contact'with j4j5, and the relay is thereby short-circuited or shunted by the conductors 5 and 6, so that it ceases to attract its armature, and the local circuit 30 being broken the lamp L is extinguished.

'Ihe connections of line 3 4 are in every way similar to those of line 1 2, the conductors going to relay l and jack J', having springs jzjs and short-circuiting contacts j6j7,

connected to wires 3 and 4 by conductors 10 and 11.v The line-lamp is L and the local circuit 31. The connections to thesignalingbattery B are numbered 12.

In order to connect any two lines together,

y the cord-circuit 17 18 19 20 is provided, havtrolled, respectively, by relays U and U. A

branch wire 28 passes from main feeder-wire 22, connected to one side of main talking-batteryB,to thetwo relays Uand U,t-akingin one winding of each only, and thence by wires 30 and 32, respectively, to the two ends 17 and 18 of the cord-circuit on one side. Similarly a branch wire 29 passes from main feeder 2l, connected to the other side of battery B, to the other coils of the relays U and U'-, and

:thence by Wires 3l and 33 to the two ends 19 and 20 of the qcord on the other side. By tracing the circuits it will be found that the relays are thus connected serially with the battery across the plug-terminals, the separated windings being of course so directed as to reinforce each other. The relayU controls by its armature u the local circuit 24, 22, B, 21, 25, u, L2, thus governing the lamp L2, and, similarly, the relay U controls by its armatureuthe circuit 26, 22, B, 21,29, 27, u, L3, thus governing lamp L3. Included in the circuits 24 and 26 are plug-seat switches p and parranged to be opened by the heels of the plugs when in their seats, so as to keep the lampcircuits normally incomplete, even when a connection is not made, thus saving battery and also preventing shortening the lives'of the lamps, which would follow their constant incandescence.

The operation of the system thus described is as follows: When subscriber calls by lifting his receiver from the hook S, current will flow from main battery B by wire 7 to one winding of relay Z, to line-wire 2,transmitterT,receiver R, hook S, line-Wire 1, the other winding of the relay Z, wire 9, and back to battery. The relay being energized causes the lamp L to receive current over the circuit B, 15, 30, L, l, Zn, 30, 16, back to battery. The operator perceiving the signal inserts answering-plug P, whereby springsj andj' are closed on their back contacts, short-circuiting the relay Z through the wires 5 and 6 and retiring the signal. At the same time the switchp has been closed bylthe removal of the plug from its seat, and the lamp L2 would light; but the relay U is now receiving current over the circuit B, 21, U, 31, P, j', wire 6,1ine-wire 1, subscribers set S R T, line-wire 2, wire 5, spring j, P, 30, U, 28, 22, and B. This holds up the armature u, and so the lamp is not lighted. Having ascertained the number desired, the plug P is inserted in jack J', (which is assumed to be connected to that line.) The relay t willr not be energized by this action, because the wires 10 13 and 11 14 are at the same potential. The relay U does not become energized,and so when the plug-seat switch p is closed the lamp L3 lights to indicate that the subscriber B has not answered. When scriber can attract the attention of the office during a connection by moving his hook, and at the termination of the conversation, when ICO IOS v IIO IZO

'he does answer by taking down his receiver, g

`both have hung` up, both lamps L2 and L3 lighting indicate the desire for discontinuation.

Having thus described my invention,what I claim, and desire to secure by Letters Patent of theUnited States, is-

l. In a telephone system, subscribers lines, means at each subscribers station for determining the fiow` of current inhis line, a relay having a portion `of its windings connected in one side of the line, and the other portion of "its windings connected in the other side of the line, a terminal connective device for the line, and means in the terminal connective device to establish a disabling shunt about eachl of the portions of the relaywindings when connection is made with/the line`,substantially as described.

2. Inatelephone system, subscribers lines and terminal connective devices therefor, a relay for each line having its windings connected in the two sides of the line so as ,to be self-balancing, a source of current-supply, a connection to each side of the line fromone side of the said source between the terminal connective device and the relay,and disabling 'shunt connections for the relay extending from the terminal connective device to the line outside of the relay, and arranged to be closed when connection is made with the line,

` substantially as described.

. 3. In a telephone system, a subscriber-s line means at the subscribers station to determine the iiow of current in the line, a signal-magnet connected in the line at the cenline, means at the subscribers station to decircuit extending between two terminal stations, a condenser in each side of said circuit, dividing it into two conductively-discontinuous but inductivelycontinuous sections, a source of current-supply, a branch connection from each side of the source to both sides of the condenser in the corresponding side of the metallic circuit, and two signal-magnets having divided windings, cach with one winding in the branch to one side of one condenser, and the other winding in the branch to the same side of the other condenser, whereby the magnets are bridged across the divided portions of the circuit, with the source in common and between their respective windings, substantially as described.

6. In a telephone system,snbscribers lines, metallic cord circuits for interconnecting them, signal-magnets for the lines, each cord having its terminals connected through the divided windings of said signal-magnets, so that one-halt` of each magnet-winding is in each side of the circuit, a source of energy `bridged across the said connections between the said magnets, and a condenser connected in shunt around each cord connection with its included windings, substantially as described.

In witness whereof I have hereunto set my hand, this 14th day of August, 1902., in the presence of two witnesses.

STANLEY A. DUVALL.

Witnesses:

R. P. FRUER, U. G. FRUER. 

